Method and apparatus for reduced feedback in implantable hearing assistance systems

ABSTRACT

A method and apparatus assists a hearing impaired person by introducing and maintaining a mechanical feedback barrier between a microphone and a transducer of an implantable hearing assistance system. In this method, mechanical sound vibrations impinging on the person&#39;s body habitus are received with an electromechanical device (e.g. microphone) disposed at a body habitus sound reception site. The body habitus sound reception site can be located within the external auditory canal, or external of the external auditory canal either subdermally or external of the scalp. The mechanical sound vibrations are converted with the electromechanical device to an amplified electrical signal. Next, the amplified electrical signal is delivered to the inner ear with a transducer operatively coupled between the electromechanical device and the middle ear or the inner ear. Finally, a mechanical feedback barrier is introduced and maintained between the sound reception site and the transducer to in mimize acoustic feedback therebetween. Preferably, this feedback barrier is established by removing, separating, or fixing, or combinations thereof, a portion of the hearing impaired person&#39;s ossicular chain (e.g malleus, incus, or stapes).

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of commonly assigned patent applicationentitled METHOD AND APPARATUS FOR REDUCED FEEDBACK IN IMPLANTABLEHEARING ASSISTANCE SYSTEMS, Ser. No. 09/327,345 filed Jun. 5, 1999, nowU.S. Pat. No. 6,267,731 which in turn is a continuation of U.S.Provisional Application Nos. 60/088,162, 60/088,276, and 60/088,319, allfiled on Jun. 5, 1998, now abandoned.

1. Field of the Invention

The present invention relates to implantable hearing systems forassisting hearing in hearing impaired persons.

2. Description of Related Art

Some implantable hearing assistance systems use a microphone located inor near the ear to convert acoustic sound energy into an electricalsignal. The electric signal is amplified, modulated and then directlycommunicated by a transducer to the inner ear to stimulate the cochleato assist hearing. Alternatively, the amplified signal is communicatedto a transducer for conversion to mechanical acoustic energy forvibratory application to the stapes of the middle ear or the cochlea.The microphone can be located externally, subdermally adjacent the ear,or within the external auditory canal. The transducer is commonlyconnected to a portion of the middle ear, known as the ossicular chain,which includes the malleus, incus and stapes. Vibrations are emittedfrom the transducer into and through the ossicular chain to the cochleaof the inner ear.

The ossicular chain facilitates forward transmission of mechanical soundvibrations from the tympanic membrane of the external auditory canal tothe inner ear. However, the ossicular chain also permits reversetransmission of mechanical sound energy to be transmitted from thetransducer of the implantable hearing assistance system, back throughthe ossicular chain to the tympanic membrane, and into the externalauditory canal. This retrograde sound transmission passes out of theexternal auditory canal and is acoustically fed back to the microphoneof the system.

This acoustic feedback limits the maximum gain which the hearingassistance system can apply to the signal received by the microphone. Inparticular, the feedback created by reverse bone conduction through theossicular chain has an inverse relationship with usable gain. Forexample, if one percent of the acoustic vibratory signal emitted by thetransducer to the stapes, or other part of the ossicular chain, is fedback through the ossicular chain and into the external auditory canal tothe microphone, the gain for the hearing assistance system is limited toroughly 100 or 40 dB. Due to the nature of the hearing losses and theacoustic limitations of these systems, a much higher gain is ideal.Accordingly, reduction or elimination of this feedback is desirable.

Moreover, these hearing assistance systems, which transmit acousticsound energy onto an ossicular chain with a transducer, are inefficientand consume power rapidly. Inefficiency results from the mechanicalforce that must be exerted by the transducer against the ossicularchain. This inefficiency causes rapid power consumption, requiringfrequent battery changes. Battery changes are, at least, inconvenientfor an externally located battery, and at worst, costly and surgically-related for a battery implanted in the middle ear or subdermally.

The importance of restoring hearing to hearing impaired persons demandsmore optimal solutions in hearing assistance systems. Ideally, animproved hearing assistance system both minimizes power consumption aswell as maximizes gain to produce a better acoustic signal for receptioninto the cochlea and the inner ear.

SUMMARY OF THE INVENTION

A method and apparatus of the present invention improves hearing for ahearing impaired person by introducing and maintaining a mechanicalfeedback barrier between a microphone and a transducer of an implantablehearing assistance system. In this method, mechanical sound vibrationsimpinging on the person's body habitus are received with anelectromechanical device (e.g. microphone) disposed at a body habitussound reception site. The body habitus sound reception site can belocated within the external auditory canal, or external of the externalauditory canal either subdermally or external of the scalp, or evensubdermally along the external auditory canal.

The mechanical sound vibrations are converted with the electromechanicaldevice to an amplified electrical signal. Next, the amplified electricalsignal is delivered to the inner ear with a transducer operativelycoupled between the electromechanical device and the middle ear or theinner ear.

Finally, a mechanical feedback barrier is introduced and maintainedbetween the sound reception site and the transducer to minimize acousticfeedback therebetween. Preferably, this feedback barrier is establishedby removing a portion of the hearing impaired person's ossicular chain(e.g malleus, incus, or stapes) or fixing a portion of the ossicularchain to prevent transmission of sound feedback. In other embodiments, aportion of the ossicular chain is not removed but merely separated sothat the procedure can be reversed if desired at a later time.

This method and apparatus of the present invention optimizes hearingimprovement by preventing unnecessary mechanical feedback that can occurthrough the ossicular chain and the external auditory canal.Interrupting the ossicular chain, or otherwise immobilizing theossicular chain, to prevent this retrograde sound transmission permitssignificant enhancement of the gain applied to the amplified electricalsignal transmitted to the stapes or inner ear. In addition, lessmechanical energy is required to transmit the acoustic energy to theinterrupted ossicular chain or cochlea than when the ossicular chainremains intact. Accordingly, this method and apparatus reduces powerconsumption and frequent battery replacement for implantable hearingassistance systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an auditory system of a human subject.

FIG. 2 is an enlarged plan view of an ossicular chain of the auditorysystem of FIG. 1.

FIG. 3 is a sectional view of an auditory system of a human subjectincorporating a first embodiment of an implantable hearing system of thepresent invention.

FIG. 4 is a sectional view of an auditory system of a human subjectincorporating a second embodiment of an implantable hearing system ofthe present invention.

FIG. 5 is a sectional view of an auditory system of a human subjectincorporating a third embodiment of an implantable hearing system of thepresent invention.

FIG. 6 is a sectional view of an auditory system of a human subjectincorporating a fourth embodiment of an implantable hearing system ofthe present invention.

FIG. 7A is a plan side view of a mounting bracket of the presentinvention.

FIG. 7B is a plan top view of a mounting bracket of the presentinvention.

FIG. 7C is a plan side view of a modified mounting bracket of thepresent invention.

FIG. 8 is a sectional view of an auditory system of a human subjectincorporating a modification of the embodiment of FIG. 3.

FIG. 9 is a sectional view of an auditory system of a human subjectincorporating another embodiment of an implantable hearing system andmethod of the present invention.

FIG. 10 a sectional view of an auditory system of a human subjectincorporating another embodiment of an implantable hearing system andmethod of the present invention.

FIG. 11 is a plan side view of a mounting bracket of the presentinvention manipulated to a pre-insertion position.

FIG. 12 is a plan side view of a mounting bracket of the presentinvention manipulated to a pre-insertion position.

FIG. 13 is a schematic plan view of a malleus fixation method of thepresent invention.

FIG. 14 is a schematic view of an incus separation and fixation methodof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The ear is the auditory organ of the body. As shown in FIG. 1, ear 20includes outer ear 22, middle ear 24, and inner ear 26. Outer ear 22, inturn, includes the pinna 30, and exterior auditory canal (externalacoustic meatus) 32 extending up to and including tympanic membrane 36.The pinna 30 is the ear flap and is visible on the exterior of the head.The exterior auditory canal extends through temporal bone 34.

Middle ear 24 begins at the interior terminus of exterior auditory canal32, the tympanic membrane 36. Middle ear 24 includes the interior sideof tympanic membrane 36 and ossicular chain 38. Ossicular chain 38, inturn, includes malleus (hammer) 42, incus (anvil) 44, and stapes(stirrup) 46.

As best seen from FIG. 2, malleus 42 includes head 52, lateral process54, anterior process 56, and manubrium 58. Malleus 42 attaches totympanic membrane 36 at manubrium 58. Incus 44 articulates with malleus42 at incudomalleolar joint 62 and includes body 64, short crus 66, andlong crus 68. Stapes 46 articulates with incus 44 at incudostapedialjoint 72 and includes posterior crus 74, anterior crus 75, capitulum 76,and base (foot plate) 79. Capitulum 76 of stapes 46, in turn, includeshead 77 and neck 78.

The base 79 of stapes 46 is disposed in and against a portion of theinner ear 26. Inner ear 26 includes cochlea 88, vestibule 90, andsemicircular canals 92. Base 79 of stapes 46 attaches to oval window 98on vestibule 90. Round window 102 is present on a more basal portion ofvestibule 90. Oval window 98 and round window 102 are considered aportion of cochlea 88 in this patent application.

Sound waves are directed into exterior auditory canal 32 by outer ear25. The frequencies of the sound waves may be slightly modified by theresonant characteristics of exterior auditory canal 32. These soundwaves impinge upon tympanic membrane 36, thereby producing mechanicaltympanic vibrations. The mechanical energy of the tympanic vibrations iscommunicated to inner ear organs cochlea 88, vestibule 90, andsemicircular canals 92, by ossicular chain 38. Thus, tympanic membrane36 and ossicular chain 38 transform acoustic energy in exterior auditorycanal 32 to mechanical energy at tympanic membrane 36.

Normally, tympanic vibrations are mechanically conducted through malleus42, incus 44, and stapes 46 to oval window 98. Vibrations at oval window98 are conducted into the fluid-filled cochlea 88. These mechanicalvibrations generate fluidic motion, thereby transmitting hydraulicenergy within cochlea 88. Receptor cells in cochlea 88 transmit thefluidic motion into neural impulses, which are transmitted to the brainand perceived as sound. Pressures generated in cochlea 88 by fluidicmotions are also accommodated by round window 102. Round window 102 is asecond membrane-covered opening between cochlea 88 and middle ear 24.

Hearing loss due to damage in cochlea 88 is referred to as sensorineuralhearing loss. Hearing loss due to an inability to conduct mechanicalvibrations through middle ear 24 is referred to as conductive hearingloss. Some patients have an ossicular chain 38 which lacks resiliency.Ossicular chains with insufficient resiliency are either inefficient ortotally fail to transmit mechanical vibrations between tympanic membrane36 and oval window 98. As a result, fluidic motion in cochlea 88 isattenuated and receptor cells in cochlea 88 fail to receive adequatemechanical stimulation. Damaged elements of ossicular chain 38 mayfurther interrupt transmission of mechanical vibrations between tympanicmembrane 36 and oval window 98.

A partially implantable hearing assistance system 100 of the presentinvention for assisting a hearing impaired person is shown generally inFIG. 3 as disposed within ear 20. It is recognized, however, that system100 may be a dual system suitable for use with either one or both of apatient's ears. System 100 includes an externally-mounted microphone102, an internal amplifier/signal processor 104, a transducer 106, andframe assembly 108. Electrical connection 110 extends from internalsignal processor 104 to transducer 106. A power supply or battery isincorporated into either external microphone 102 or internal signalprocessor 104.

External microphone 102 is a conventional microphone or otherelectromechanical device for converting acoustic sound energy into anelectrical signal. In one embodiment external microphone may be ahandheld or other similarly configured radio frequency linked systemoperatively coupled with other components of the hearing assistancesystem. In another embodiment, external microphone 102 is shaped andsized for removable attachment about the ear 20, exterior to skin 120.Internal amplifier 104 includes signal processing circuitry and iseither directly electrically connected to microphone 102 through skin120 or includes a coil transformer for electromagnetically receiving anelectrical signal from external microphone 102. Internal amplifier 104is preferably attached to the patient's skull below skin 122 subdermallywithin space 124. Both microphone 102 and amplifier 104 are miniatureelectronic modules well known in the art of hearing assistance systems.

Transducer 106 is disposed within middle ear space 24 and securedagainst a wall of middle ear space 24 or within mastoid cavity 126against mastoid bone 34 with frame assembly 108 using one or morefasteners. Finally, transducer 106 is operatively connected to stapes46. Electrical connection 110, which extends from amplifier 104 totransducer 106, operatively communicatively couples transducer 106 toamplifier 104.

With system 100, acoustic sound vibrations impinging on or about outerear 22 are received by microphone 102 and converted to an electricalsignal and transmitted to amplifier 104. After amplification andmodulation, the electrical signal is communicated to transducer 106 viaelectrical connection 110. In response to the electrical signal,transducer 106 produces an acoustic vibratory signal that is applied tostapes 46 and ultimately, cochlea 88 via oval window 98. Microphone 102,amplifier 104, and transducer 106 and their communication with eachother may be of a type generally known to those skilled in the art,although improved transducer means are contemplated within the scope ofthis invention to facilitate improved implant procedures, to minimizeinvasiveness, and to improve the reliability of the transducer.

Finally, system 100 and the method of the present invention includesintroducing and maintaining a mechanical feedback barrier to preventmechanical or acoustic feedback from transducer 106 to microphone 102.This feedback barrier is preferably implemented by interruptingossicular chain 38. However, freezing movement of ossicular chain 38 orotherwise isolating microphone 102 and transducer 106 frommechanical/acoustic feedback through ossicular chain 38 can also providethe necessary barrier. In addition, the feedback barrier can beaccomplished through various sound dampening and sound isolationmaterials and/or techniques placed appropriately about, or between, oneor more portions of the ossicular chain.

As shown in FIG. 3, ossicular chain 38 including malleus 42, incus 44,and stapes 46 has been interrupted by disconnecting incus 44 from stapes46. This interruption creates a barrier to prevent mechanical feedbackof acoustic sound energy from transducer 106 through ossicular chain 38and external auditory canal 32, to microphone 102. Of course, thedisarticulation of ossicular chain 38 could occur any place betweentympanic membrane 36 (umbo) and transducer 106.

In addition, the transducer 106 can be directly coupled to oval window98 or round window 102 of cochlea 88 by prior removal of stapes 46. Inthat embodiment, removal of stapes 46 acts to disarticulate theossicular chain 38 to prevent feedback and permits malleus 42 and incus44 to remain in place. Maintaining a connection of at least malleus 42(and optionally incus 44) to tympanic membrane 36 may also aid inpreventing damage from acoustical trauma, since maintaining malleus 42further enables the natural musculoskeletal defense mechanisms toprotect against acoustical trauma.

While removal of ossicular chain 38 has taken place in some priormethods and systems, such removal typically occurs to solve middle earconduction-type hearing loss problems, or to remove diseased tissue andossicular bones. Sensorineurally impaired patients have hearingimpairments not caused by dysfunction of the middle ear conductionchain, i.e. ossicular chain 38. Accordingly, sensorineural impairmentsdo not dictate removal of ossicular chain 38. In fact, some in the artbelieve it unethical, or at least inappropriate, to remove a healthyossicular chain to remedy a hearing impairment. Accordingly, removing orfreezing movement of a portion of ossicular chain 38, or otherwiseisolating ossicular chain 38 from an implantable middle ear system, suchas system 100, in sensorineurally impaired patients is a unique andcounter-intuitive solution to reduce acoustic feedback and improve thegain of the hearing assistance system.

While maintaining ossicular chain 38 intact (in order to preserve ahealthy ossicular chain 38 despite a hearing impairment) may appear tobe less intrusive, a method of the present invention recognizes thatunconditionally maintaining the chain can dramatically reduce the gainachieved by the implantable middle ear hearing assistance system due tothe feedback phenomenon described above. In this manner, the choice tomaintain ossicular chain 38 can actually impede improving hearing inhearing impaired patients, particularly those with sensorineuralimpairment However, in certain circumstances according to each patient'smiddle ear morphology, this invention may not be limited to the class ofpatients which only includes those suffering from sensorineuralimpairment. Accordingly, the method of the present invention interruptsossicular chain 38 to prevent feedback, particularly for sensorineurallyimpaired patients.

Another hearing assistance system 130 of the present invention is shownin FIG. 4. System 130 includes electromechanical device 132 (e.g.microphone), amplifier/ signal processor 134, transducer 136, and frameassembly 138 with electrical connections 140 and 142. Microphone 132 hasfeatures and attributes similar to microphone 102, except for itsimplantation below skin 120 subdermally. Signal processor 134 includesan amplifier and signal processing characteristics for amplifying andfiltering an electrical signal from microphone 132. A battery may beincorporated with signal processor 134 as shown, or optionallyincorporated externally adjacent ear 120, or incorporated withmicrophone 132. Transducer 136 has features and attributes similar totransducer 106 and is, likewise, connected to stapes 46 via head 77. Asin the embodiment of FIG. 3, transducer 136 can alternatively beoperatively coupled to round window 102 or oval window 98 of cochlea 88.Signal processor 134 is secured to the mastoid bone 34 within cavity126. Electrical connection 140 extends between microphone 132 andprocessor 134 while electrical connection 142 extends between, andelectrically couples processor 134 and transducer 136. As shown in FIG.4, incus 44 was removed from ossicular chain 38 to introduce andmaintain a feedback barrier against transmission of mechanical soundenergy through ossicular chain 38 from transducer 136 to externalauditory canal 32, and ultimately, microphone 132. Of course, as earliernoted, other portions can be removed from ossicular chain 38 in place ofremoving incus 44 to effect the disarticulation and interruption ofossicular chain 38 to prevent acoustic feedback.

This method and system 132 enjoys advantages and features similar tosystem 100 as a result of the introduction of an acoustic feedbackbarrier between microphone 132 and transducer 136.

Another partially implantable hearing system 150 of the presentinvention is shown in FIG. 5. System 150 includes a single unitimplantable device 152, including a microphone, amplifier, and battery.System 150 further includes transducer 156, frame assembly 158, andelectrical connection 160. Device 152 is removably secured within theauditory canal, for example in external auditory canal 32, whiletransducer 156 is supported within the middle ear cavity 24 byconnection assembly 158 secured against mastoid bone 34 within cavity126. As before, transducer 156 is secured to head 77 of stapes 46 or,alternatively, secured to the oval or round windows of cochlea 88 in theabsence of stapes 46. As in the other systems 100 and 130,disarticulation of the ossicular chain 38 creates a feedback barrier toprevent a retrograde transmission of sound energy from the transducer136 through the external auditory canal 32 to microphone of device 152.As shown, ossicular chain 38 has been interrupted, or disarticulated, byseparating incus 44 from stapes 46. However, disarticulation could takeother forms, including removal of incus 44, removal of malleus 42 orremoval of stapes 46, or any combination thereof. Moreover, as discussedfurther below in connection with FIG. 9, disarticulation can includecutting or removing a portion of the incus to interrupt the ossicularchain, as well as other techniques.

In another embodiment of the present invention shown in FIG. 6, ahearing assistance system 170 includes features and attributes similarto system 100 shown in FIG. 3 by having an external microphone orelectromechanical device 172 and an internal amplifier 174. However, insystem 170, an electrical stimulator, such as a piezoelectricaccelerometer 176 is mounted within mastoid cavity 126, as shown inphantom, or on the head of malleus 142. Electrical stimulator 176includes leads 178 for electrical connection to various portions ofcochlea 88 for electrical stimulation thereof to produce neural impulsescorresponding to the acoustic sound received by microphone 172, as knownin the art. Electrical connection 180 operatively couples amplifier 174to stimulator 176. Finally, alternatively to electrical stimulator 176,mechanical stimulator 180 can be operatively coupled to round or ovalwindow of cochlea 88. As shown in FIG. 6, as in the other of the presentinvention systems 100, 130, and 150 a feedback barrier is introducedbetween microphone 172 and stimulator 176 or 180 by disarticulation ofossicular chain 38. Disarticulation of the ossicular chain isaccomplished by removal of the stapes 46 or separation of ossicularchain 38 elements (without their removal). Of course, the othermicrophone and amplifier combinations as shown in FIGS. 4 and 5 can beimplemented with an electrical stimulator, such as stimulator 176 (orthe alternative mechanical stimulator 180).

Implementing the method of the present invention in the embodiment ofFIG.6 insures no inadvertent acoustic/mechanical feedback occurs throughossicular chain 38 to microphone 172 from stimulator 176, 180 or fromcochlea oval window 98 even though direct stimulation of cochlea 88occurs apart from ossicular chain 38.

FIGS. 3-5 each show a mounting bracket (108, 138, 158) for placing atransducer in contact with an auditory element of the stapes. Whilebrackets known in the art can be used, the method and systems of thepresent invention may also use a bracket of the type similar to thatshown in FIGS. 7A-7C. FIGS. 7A, 7B, and 7C show a bracket system 200having a transducer 202 attached to the single bracket support 204. Thesingle bracket support 204 includes an opening 206. A bone screw 208 orsimilar attaching means passes through the oblong opening 206 and allowsfor independent adjustment of the distance between the support mountingscrew 208, which is typically a bone screw, and the transducer 202. Suchadjustment allows flexibility in that the single bracket support can bemounted with respect to different auditory elements, such as the malleus42 and the stapes 46, respectively, in a patient population havingvarying anatomical features within the middle ear 24.

The shape of single bracket support 204 in this embodiment is more orless a flat plate. The transducer 202 is coupled to the flat plateeither adhesively, mechanically or otherwise, to produce a singlecomponent. It should be noted that other configurations are possible,depending on patient anatomy and other factors. A generally L-shapedbracket, a rectangular-shaped bracket, or any other shaped bracket thatfacilitates mounting of transducer 202 can be used in place of thesingle bracket support 204. The bone screw 208 couples the singlebracket support 204 to the mastoid bone 34. Other types of fasteningtechniques can also be used. For example, single bracket support 204 canbe shaped with a flange that could be attached to the mastoid bone 34.The single bracket support 204 can be moved linearly and rotated withrespect to the bone screw 200 to position the transducer 202 in aselected position with respect to one of the elements of the middle ear.

FIG. 7C shows an embodiment having a universal connector 210 placedbetween the transducer 202 and the single bracket support 204. Theuniversal connector 210 may also be placed between the two portions ofthe single bracket support 204. The universal connector 210, such as aball and socket joint, allows further adjustability and 360-degreemovement to position the transducer 202 against respective auditoryelements 42 and 46.

As shown in later FIGS. 8 and 9, bracket system 200 can include multiplebracket supports 204 each having a universal connector 210 foradjustability. In addition, the bracket systems 200 can include multipleslots such as slot 206, laterally spaced from each other and havingdifferent lengths, to permit flexibility in selecting the length atwhich bracket support 204 extends outwardly from its point of attachmentto the mastoid bone or middle ear structure.

As shown in prior FIGS. 3-5, a fastener, such as bone screw 208 isattached to the mastoid bone 34 to secure the bracket 200 within middleear space 24 and transducer 202 adjustably in contact with stapes 46. Ofcourse, bracket 202 also permits transducer 202 to be adjustably incontact with the malleus 42 via universal joint 210. The varioustransducer and mounting means of the invention facilitate a trans-canalimplant procedure by which portions of the device of the invention areimplanted, in one embodiment, through the auditory canal and thetympanic membrane into the middle ear.

Another system 220 and method of the present invention is shown in FIG.8. System 220 includes system 100 as shown in FIG. 3 and furtherincludes securing incus 44 into a fixed position within the middle ear.Accordingly, system 200 further includes additional bracket support 221(with universal joint 222) affixed to long process 68 of incus 44.Bracket 221 secures incus in a position separated from stapes 46 toprevent retrograde transmission of sound along the ossicular chain.Bracket 221 could also be implemented to secure incus 44, malleus 42, orstapes 46 in a configuration, where none of the auditory elements(incus, malleus, stapes) have been removed nor separated from eachother, to effectively freeze the ossicular chain preventing transmissionof sound along the chain. In this latter configuration, incus 44 remainsconnected to stapes 46 (as shown in FIG. 1) and bracket 221 is connectedto malleus 42, incus 44, or stapes 46 with sufficient tension to freezemotion of the ossicular chain to establish a mechanical feedbackbarrier.

Another method and system of the present invention for maintaining amechanical barrier against feedback is illustrated in FIG. 9. As shownin FIG. 9, malleus 42, incus 44 and stapes all remain within middle earspace 24. However, incus 44 includes long process 68, which has beensurgically cut (e.g. by laser or other means) into first portion 240 andsecond portion 242. As further shown in FIG. 9, system 250 of thepresent invention includes bracket support frame 252, bracket extensions254 and 256, transducer 258 and fastener 260.

Implementing bracket system 250 in a method of the present inventionincludes interrupting the ossicular chain to prevent feedback by cuttingincus 44 into two separate portions 240 and 242. This method can be usedin conjunction with the hearing systems of FIGS. 2-5 and 8 to establisha mechanical feedback barrier wherein cutting incus 44 is substitutedfor: (1) removing incus 44; (2) separating incus 44 from the stapes 46or malleus 42; or (3) any other method of interrupting the ossicularchain, such as freezing or fixing the position of the ossicular chainwithout cutting or separating elements of the chain.

Next, the method includes mounting bracket system 250 against mastoidbone 34 with fastener 260 and manipulating bracket extension 254 toplace transducer 258 in contact with portion 240 of long process 68 ofincus 44. Next, transducer 258 is operatively secured or positionedagainst the exposed end of portion 240 with an adhesive or other knownfastening means. The cut through long process 68 of incus 44 is made sothat a separation of at least about 2 to 3 millimeters is maintainedbetween the ends of incus portions 242 and 240, accounting for atransducer thickness of about 0.5 millimeters mounted on the end ofincus portion 240. This separation distance prevents mucosal growth orbone re-growth that could otherwise act to rejoin incus portions 240 and242.

With this configuration, transducer 258 can receive an electrical signaland transmit to incus portion 240 a sound vibration signal for deliveryto inner ear 26 via stapes 46. Transducer 258 receives its signal froman electromechanical device (e.g, microphone) and/or amplifier disposedin one of the configurations shown in FIGS. 2-5, 8, and 10.

This method preserves incudostapedial joint 72 so that naturaltransmission occurs from incus 44 to stapes 46 and so that in the eventthe procedure needs to be reversed, incudostapedial joint need not bere-created but rather incus portions 240 and 242 can simply be fusedtogether. This method also preserves the lenticular process on stapes46. In short, this method permits interruption of the ossicular chain ina minimally invasive and reversible manner, while enhancing hearingassistance.

While feedback can be prevented with portion 240 of incus 44 beingmerely separated from portion 242, it is preferred, as shown, tooptionally further secure incus portion 242 into a fixed position withbracket extension 256 to insure incus portion 242 remains separated fromportion 240 at an adequate minimum separation distance (e.g. about 2-3millimeters) to prevent tissue reconnection or inadvertent contactbetween incus portions 240 and 242.

As shown in FIG. 10, a human auditory canal is depicted with system 270and a method of the present invention incorporated therein. System 270for implementing a method of the present invention includes bracketsystem 200 (see FIGS. 7A-7C) having transducer 202, bracket support 204,positioning slot 206 (not seen in FIG. 10), fastener 208, and universalconnector 210. System 270 further includes malleus fastener 272,microphone 274, amplifier/electronics unit 276, lead wires 278. Finally,the method includes formation of slit or hole 280 in tympanic membrane36.

First, in this method, microphone 274 preferably is located alongexternal auditory canal 24 in contact with the canal wall 282. Thisconfiguration takes advantage of the known sound filtering andamplification characteristics and localization effects of the outer ear22 (including the structure shown in FIG. 1 extending from the pinna 30to the tympanic membrane 36) of the human auditory system. Thismicrophone location can be implemented to substitute for any of themicrophone locations of the systems shown and described relative toFIGS. 2-6 and 8-9. Microphone 274 is preferably a directional microphonewhich receives sound transmission traveling inwardly through theexternal auditory canal 32 while excluding sound transmission travelingoutwardly through the external auditory canal 32.

In addition, as will be further described later, microphone 274 can belocated within middle ear space 24 behind tympanic membrane 36,preferably on malleus 42 as shown in phantom in FIG. 10. When microphone274 is an acoustic microphone, this placement also takes advantage ofthe sound filtering, amplification, and localization effects of outerear 30.

Second, amplifier/electronics unit 276 is placed in external auditorycanal 32 or another location available (e.g. pectoral, or outside skull)to avoid a mastoidectomy procedure. Placement of amplifier/electronicsunit at a pectoral location permits the use of long life batterieshaving a size normally unsuitable for middle ear implantation and/orpermits easier battery replacement. Amplifier 276 is electricallyconnected to microphone 274 with lead wires 278 (shown in phantom formicrophone placement on malleus 42). Lead wires 278 pass through slit282 (or slit 280) of tympanic membrane 36 for connection to transducer202.

The following method of insertion is used for implanting at leasttransducer 202, electromechanical device 274 (in phantom in FIG. 10) orany other component hearing assistance system 270 within middle earspace 24.

First, transducer 202 is affixed to a mounting bracket prior toinsertion in the middle ear. The mounting bracket system 200 preferablyincludes a universal joint 210 disposed between a first elongate portion(support 204) and a second elongate portion (transducer 202). The secondportion 202 commonly includes both a support and the transducer affixedtogether.

Prior to insertion in the middle ear, first portion 204 and secondportion 202 of mounting bracket system 200 are manipulated to be alignedin an elongate configuration generally parallel along a single axis. Theconfiguration can include either arranging first portion 204 and secondportion 202 of the mounting bracket 200 in a side-by-side relationshipgenerally parallel to each other as shown in FIG. 11, or as shown inFIG. 12, arranging first portion 204 and second portion 202 of mountingbracket 200 in an end-to-end relationship (aligned generally parallelalong a single axis). In general, first portion 204 and second portion202 need not be generally parallel but can be in any configuration (e.g.45 or 90 angle) that facilitates insertion of mounting bracket 200 intothe middle ear space 24 through tympanic membrane 36.

Next, using surgical techniques known to those skilled in the art, a lowprofile entry slit or hole 280 is created in tympanic membrane 36. Withthe mounting bracket system 200 and transducer in one of the above lowprofile configurations (see, e.g., FIG. 11), mounting bracket 200 isinserted into and through slit 280 in tympanic membrane 36. After firstportion 204 and second portion 202 of mounting bracket 200 arereconfigured into an operative in-use configuration (e.g. 30, 60 or 90angles), bracket 200 is then mounted against a wall of the middle earspace or against mastoid bone 34 as shown. In a system, such as thatshown in FIG. 10 (microphone 274 and electronics unit 276 external tomiddle ear), middle ear implantation of transducer 202 via tympanicmembrane 36 avoids a mastoidectomy. After insertion of the transducer202 through slit 280, tympanic membrane 36 will heal appropriately.

This method permits insertion of a device such a bracket/transducercombination into the middle ear without a mastoidectomy where thebracket/transducer can be deployed in the middle ear space in aconfiguration different than the configuration used for insertionthrough tympanic membrane.

Of course, in the embodiment where microphone 274 is mounted behindtympanic membrane 36 on malleus 42 (shown in phantom), microphone 274can be inserted through tympanic membrane 26 without a mounting bracket200. Instead, microphone 274 may include adhesive means for mounting tomalleus 42 or other fastening system.

Moreover, the method of insertion/implantation through tympanic membrane36 according the present invention is not limited to the use of bracket200. Accordingly, any transducer or component of a hearing assistancesystem can be inserted through tympanic membrane 36 without a bracketlike bracket system 200 for implantation in middle ear 24. For example,the other systems shown in FIGS. 2-6, 8-9 that have at least atransducer or electromechanical device or component of a hearingassistance system can be implanted with the just described method ofinsertion instead of using a mastoidectomy.

In addition, insertion through tympanic membrane 36 can optionally becombined with other features of the present invention such as securingan auditory element into a fixed position. Accordingly, as shown in FIG.10, malleus 42 is secured in a fixed position by fastener 272 to preventtransmission of feedback sound energy along the ossicular chain. Ofcourse, other fastening means such as brackets, like bracket system 200,sutures, bone cement and adhesives can be used.

In addition, the cochlea stimulator embodiments of FIG. 6 can bemodified so that microphone 172 is replaced with a microphone locatedbehind the tympanic membrane 36 within middle ear space 24, such atmicrophone 274 (shown in phantom in FIG. 10) attached to malleus 42.

The method and system of the present invention improves hearingassistance for the hearing impaired in implantable hearing systems usinga microphone by neutralizing acoustic feedback through the ossicularchain and external auditory canal. The method can be employed invirtually all combinations of implantable systems having microphoneslocated externally, subdermally, or within or along the externalauditory canal. Elimination of acoustic feedback through the ossicularchain produces better gain in these systems, and reduces powerconsumption since less mechanical force is required to transmit acousticsignals into the inner ear (via stapes or not) with an interruptedossicular chain. Moreover, the methods of the present invention areminimally invasive procedures using tympanic insertion of a transduceror mounting bracket and/or reversible procedures using separation of theossicular chain without removal of any auditory elements or withoutdismembering any joints such as the incudostapedial joint

A further method and system of ossicular chain fixation of the presentinvention for reducing mechanical feedback is shown in FIG. 13. FIG. 13shows auditory system 20 including external auditory canal 32, bone 35(e.g. temporal bone), tympanic membrane 36, malleus 42, incus 44, andstapes 46. In this method, hole 302 is drilled through bone 35(preferably temporal bone near the zygomatic root) until malleus 42 isvisualized. Next, laser 304 is used to cut a hole in the head of malleus42 for receiving fastener 300 (e.g., screw, rivet, pin, etc.). Fastener300 is then inserted into and through hole 300 and securely fixed intohead of malleus 42 with a portion (e.g. Head) of fastener 30 remainingwithin bone 35. This arrangement securely fixes head of malleus 42 tobone 35, thereby restraining movement of malleus 42 and thereby reducingand/or preventing mechanical feedback through ossicular chain accordingthe method of the present invention previously described. As seen inFIG. 13, in this embodiment, the elements of the ossicular chain are notseparated from each other although separation of one or more elements ofthe ossicular chain may optionally be done in combination with fixationof malleus by fastener 300.

In addition, other methods of access to malleus 42 for fixing fastener300 thereon can be used such as a mastoidectomy, or access through awall of the external auditory canal, or other methods available to thoseskilled in the art. FIG. 13 also shows hole 303 in phantom to representthe possible need for a wider hole to accommodate a head of fastener 300as necessary.

Finally, in another embodiment of a method of fixation and separation ofthe ossicular chain of the present invention, a combined fixation andseparation system 350 operates to separate incus 44 from stapes 46 (e.g.at incudostapedial joint) and securely fix incus 44 to restrain itsmovement. As shown in FIG. 14, system 350 is implemented with malleus42, incus 44, and stapes 46, all of which are visible (except stapes 46)through an access hole 351 provided by a partial or whole mastoidectomyor other surgical techniques for gaining access to the ossicular chain.System 350 includes sensor 352 with accompanying support bracket 354,stapes driver 356 with accompanying support bracket 358, and incusfixator 360. Fixator 360 includes supporting bracket 362, extensionsupport 364 having a selectively variable position, fastener 366,fixator arm 368 and ring 370.

In use, stapes 46 is separated from incus 44 as shown. Sensor 352 anddriver 356 are operatively coupled to malleus 42 and stapes 46;respectively, using known techniques and/or supporting brackets 354 and358. Sensor 352 and driver 356 are operatively coupled to each otherand/or electronics unit 380 via electrical wires, and can omit orinclude further combinations of intervening signal processing,amplification, filtering and gain compression components as necessary.

Ring 370 of incus fixator 360 is maneuvered about long process 68 ofincus 44, operating as a lasso to slip over the free end of incus 44 toeffectively grasp incus 44, creating an operative coupling of fixatorarm 368 to incus 44. Supporting bracket 362, selectively variableposition extension arm 364, and fastener 366 are manipulated into aselected fixed position to maintain incus 44 in a fixed positionseparated from stapes 46. This arrangement prevents mechanical feedbackthrough the ossicular chain in accordance with the previously describedmethods of the present invention.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritor scope of the present invention. However, what is disclosed includesas a minimum the following various concepts. A method and apparatusassists a hearing impaired person by introducing and maintaining amechanical feedback barrier between a microphone and a transducer of animplantable hearing assistance system. In this method, mechanical soundvibrations impinging on the person's body habitus are received with anelectromechanical device (e.g. microphone) disposed at a body habitussound reception site. The body habitus sound reception site can belocated within the external auditory canal, or external of the externalauditory canal either subdermally or external of the scalp. Themechanical sound vibrations are converted with the electromechanicaldevice to an amplified electrical signal. Next, the amplified electricalsignal is delivered to the inner ear with a transducer operativelycoupled between the electromechanical device and the middle ear or theinner ear. Finally, a mechanical feedback barrier is introduced andmaintained between the sound reception site and the transducer tominimize acoustic feedback therebetween. Preferably, this feedbackbarrier is established by removing, separating, or fixing, orcombinations thereof, a portion of the hearing impaired person'sossicular chain (e.g malleus, incus, or stapes). In another embodiment,a method and apparatus assists a hearing impaired person by introducingand maintaining a mechanical feedback barrier between a microphone and atransducer of an implantable hearing assistance system. In this method,mechanical sound vibrations impinging on the person is body habitus arereceived with an electromechanical device (e.g. microphone) disposed ata body habitus sound reception site. The body habitus sound receptionsite can be located within the external auditory canal, or external ofthe external auditory canal either subdermally or external of the scalp.The mechanical sound vibrations are converted with the electromechanicaldevice to an amplified electrical signal. Next, the amplified electricalsignal is delivered to the inner ear with a transducer operativelycoupled between the electromechanical device and the middle ear or theinner ear. Finally, a mechanical feedback barrier is introduced andmaintained between the sound reception site and the transducer tominimize acoustic feedback therebetween. Preferably, this feedbackbarrier is established by removing, separating, or fixing, orcombinations thereof, a portion of the hearing impaired person'sossicular chain (e.g., malleus, incus, or stapes). In anotherembodiment, a method and apparatus assists a hearing impaired person byintroducing and maintaining a mechanical feedback barrier between amicrophone and a transducer of an implantable hearing assistance system.In this method, mechanical sound vibrations impinging on the person'sbody habitus are received with an electromechanical device (e.g.microphone) disposed at a body habitus sound reception site. The bodyhabitus sound reception site can be located within the external auditorycanal, or external of the external auditory canal either subdermally orexternal of the scalp. The mechanical sound vibrations are convertedwith the electromechanical device to an amplified electrical signal.Next, the amplified electrical signal is delivered to the inner ear witha transducer operatively coupled between the electromechanical deviceand the middle ear or the inner ear. Finally, a mechanical feedbackbarrier is introduced and maintained between the sound reception siteand the transducer to minimize acoustic feedback therebetween.Preferably, this feedback barrier is established by removing, separatingor fixing, or combinations thereof, a portion of the hearing impairedperson's ossicular chain (e.g., malleus, incus, or stapes).

What is claimed is:
 1. A partially implantable apparatus for improvingthe hearing of a hearing impaired subject without causing feedbackthrough the ossicular chain of the subject, comprising: an artificialsensing transducer for sensing air conducted signals external to themiddle ear, the transducer configured and arranged for dispositionsubdermally along and in contact with the external auditory canal; inputand output transducer means adapted for cranial location for mediatingmechanical and electrical signals having controlled amplificationcharacteristics, the input and output transducer means havingelectromechanical linkage means for operatively communicatively couplingthe artificial sensing transducer to the inner ear of the subject totransmit signals therebetween without feedback of mechanical soundenergy from the inner ear to the artificial sensing transducer throughthe ossicular chain and the external auditory canal; and means formaintaining the malleus of the middle ear in a fixed position to preventtransmission of sound energy along the ossicular chain.
 2. The apparatusof claim 1, wherein the maintaining means further comprises: a bracketfor securing the malleus against the mastoid bone.
 3. The apparatus ofclaim 1, wherein the maintaining means further comprises: a suture forsecuring the malleus against the mastoid bone.
 4. The apparatus of claim1, wherein the transducer is a piezoelectric transducer.
 5. Theapparatus of claim 1, wherein the transducer is an electromagnetictransducer.
 6. The apparatus of claim 1, wherein the electromechanicallinkage means further comprises: a connection assembly adapted to besecured to a portion of the subjectAEs ossicular chain.
 7. The method ofclaim 6, wherein the connection assembly further comprises a bracket. 8.The method of claim 6, wherein the connection assembly further comprisesa hanger.
 9. The method of claim 6, wherein the connection assemblyfurther comprises a combination mounting bracket and removable portion.